iPhone 8 can only detect 5GHz WiFi. No 2.4 GHz reception.

I’m trying to connect to a WiFi network via Settings >> WiFi on my iPhone 8 and it only shows 5GHz networks and no other networks including Personal Hotspots (I did a research and found out that Personal Hotspot works at 2.4GHz). WiFi works great on 5GHz networks, but it’s very difficult to find one in my area and the phone becomes pretty much unusable. Other devices like a MacBook Pro and an iPhone 6, 6S, 7 - all detect lots of 2.4GHz and 5GHz networks in the same location at the same time.

Here’s what I know for sure:

• iPhone 8 64Gb Gold iOS 12. The IMEI matches the SIM tray. Not stolen, not locked.
• Tested in different areas - both with lots of different WiFi networks and in a remote field with only one access point. The problem is NOT caused by radio interference;
• Tried Reset Network Settings 3 times - problem still exists;
• Tried Erase All Content and Settings and set up as a new iPhone twice - problem still exists;
• Tried downgrading to 11.4.1 - problem still exists;
• GPS works;
• Bluetooth works;
• Cellular, LTE and everything else works;
• Apple 1-year warranty status: expired;

Here’s what I’m not sure about:

• According to coconutBattery the phone is 385 days old, but the battery is only 7 cycles old. Not sure if the battery has been replaced. Not sure if the phone has ever been disassembled. The seller told me that the device hadn’t been used during all this time and was never opened. Still cannot trust 100%.
• Not sure about the time when the problem first appeared. I received the device like this with iOS 12.

The question is: is the WiFi diversity antenna replacement likely to help restore the 2.4GHz reception? (Looking for opinions based on personal experience, not speculation)

How likely is it to solve the problem with given symptoms?

Is it a software, the WiFi chip or the antenna failure?

Thank you Minho for a great advice!

I did open up the device and it looks like nobody has ever touched it inside.

I did check all 3 antennas. I did unplug them, removed, inspected under a microscope and put everything back together. They all looked ok and untouched. I even tried unplugging both antenna connectors from the motherboard and removing the top left antenna while searching for WiFi networks. The WiFi reception became worse, but even without the antennas it successfully connected to my nearest 5GHz network. Even Bluetooth works without those antennas. But the 2.4 WiFi doesn’t work even when I put the phone right on top of the router.

During the inspection however, I started a WiFi search and tried applying pressure all over the board and the connectors and for a moment it did find a new 2.4GHz Wifi called “Philips-DIRECT” which is a TV in the other room. But then it quickly disappeared. I managed to find it once again, but still couldn’t detect what had caused it to appear.

So my next step is to replace a wifi antenna, but I don’t know which one. The top left antenna that looks more like a plastic cover affected my 5GHz reception. As I removed it, the 5GHz signal weakened. Also the problem might be in the motherboard. I checked my serial in the replacement program, but it is not eligible.

Any advice on which antenna to replace?